A drug delivery system is synthesized by using poly(N-isopropylacrylamide)-b-poly(L-alanine) (PNIPAAm-b-PAla) block copolymers with different molecular weights, in which the molecular weight can be controlled by adjusting concentration ratio of the PNIPAAm-NH2 and L-Ala-NCA. The lower critical solution temperature (LCST) of the copolymer is a little lower than that of the pure PNIPAAm. Furthermore, with the increase of chain length of the poly(L-alanine) block, the LCST shifts to much lower value. The FT-IR, DSC and TEM characterizations of the products indicated that the amphiphilic PNIPAAm-b-PAla block copolymer can self-assemble into a spherical core-shell micelle structure. This micelle carrier exhibits a reversible phase transition within a very narrow temperature range (about 4 C). This drug delivery system not only shows good dissolution and hydrophilicity, but also is biodegradable. As a drug carrier of adriamycin (ADR), the PNIPAAm-b-PAla and ADR can form the core-shell micelle easily without precipitation, which prolongs the release time (it is more than 20 h here) of the ADR. Accordingly, this PNIPAAm-b-PAla copolymer is an excellent carrier for controlling drug delivery and release. (C) 2010 Elsevier B.V. All rights reserved.